The present disclosure is directed to melt furnace systems. More specifically, the disclosure is directed to tilt rotary furnace systems and methods for operating tilt rotary furnace systems.
Tilt rotary furnaces are used in processes like aluminum melting because they provide flexibility in metal tapping by furnace tilting. Three advantages include 1) they can operate with a much lower process temperature since a charge material can be removed by tilting (contrary to fixed-axis rotary furnaces where the process temperature is often well beyond what is needed for melting the charge material in order to liquefy the added flux to be removed after each cycle), 2) they can be emptied more thoroughly, and 3) they can reduce oxide formation on the charge material.
However, charge material distribution in a tilt rotary furnace is not uniform due to the tilt. Due to gravity, the charge material flows toward the end of the furnace above an edge of the furnace. Such load distribution is suboptimal to the conventional means of heat delivery, especially oxy-fuel burners, which tend to deliver relatively high heat flux in the flame vicinity. Known burners for use in tilt rotary furnaces lack the control to provide a heat release pattern corresponding to the positioning and depth of the charge material. Thus, these known burners provide too little heat to certain portions of the charge material or they waste heat by providing too much heat to other portions of the charge material. Because of this, known tilt rotary furnaces having known burner arrangements may have increased oxidation of metal and need to be cleaned frequently.
U.S. Pat. App. Pub. No. 2009/0004611 A1 is directed to a combustion method. In the method, an industrial furnace is heated by one or more burners. Examples of the furnaces include steel reheating furnaces, aluminum melting furnaces, glass melting furnaces, cement kilns, lead melting furnaces, copper melting furnaces, and iron melting furnaces. Fuel (for example, any combustible fluid) and primary oxidant (a fluid having an oxygen concentration of at least 50 volume percent) are provided to the furnace through the one or more burners. The fuel and primary oxidant are provided at flow rates having a stoichiometric ratio of primary oxygen to fuel of less than 70 percent. The fuel and primary oxidant are provided at velocity of 100 feet per second or less. Secondary oxidant is injected through a lance. Heat generated in a combustion reaction radiates to the charge to heat the charge. The heat radiates directly or indirectly through furnace gases and walls and very little heat is passed by convection. This Application discloses nothing about the selective adjustment of heat flux to achieve uniform heating to a melt with uneven depth using burners at the same firing rate.
U.S. Pat. No. 5,755,818A (corresponding to EP 0 748 982 B1) (the '818 patent) is directed to a method of staged combustion. The method is similar to that which is discussed in the '611 application; however, fuel and primary oxidant are provided at velocity of at least 100 feet per second. Like the '611 application, heat generated in a combustion reaction radiates to the charge to heat the charge, and the heat radiates directly or indirectly through furnace gases and walls and very little heat is passed by convection. Similarly, the '818 patent does not teach how to adjust the flame shape and length for different applications and different operational conditions.
U.S. Pat. No. 5,609,481 (corresponding to EP 0 748 994) (the '481 patent) is directed to a method of heating or melting a charge of material in a direct-fired furnace. In the method, the charge is heated by radiant heat from a direct-fired burner. A charge-proximal gas for increasing or decreasing oxidation is introduced between the direct-fired burner and the charge. The charge-proximal gas forms a stratum separating combustion products from the charge. The stratum can be adjusted to control oxidation of the charge. To maintain the stratum, fuel, oxidant, and the charge-proximal gas are introduced at velocities below 50 feet per second. The '481 patent suffers from several drawbacks. For example, the strata can be interrupted by mixing of the charge thus limiting the ability to distribute heat within the charge and reducing the ability to utilize convective heating.
The disclosure of the previously identified patents and patent applications is hereby incorporated by reference.
It is desirable in the art to provide methods for controlled heating of melt furnace systems which result in greater uniformity in melting, reduced oxidation of charged material, and more thorough emptying with fewer cleaning cycles.